JP4185523B2 - Electroless nickel plating film and machine part having this film - Google Patents

Description

  The present invention relates to a nickel-based electroless plating film and a machine part using the film. More specifically, the present invention relates to a plating film exhibiting high hardness in a wide temperature range from room temperature to high temperature and excellent in sliding properties.

  Unlike electroplating, an electroless plating film can form a uniform plating film only by immersing an object to be plated in a plating bath, and is excellent in productivity. In electroless plating, a film containing at least one of phosphorus and boron in nickel has a relatively high hardness and is used for surface treatment of various machine parts.

As a surface treatment for a sliding component, for example, a Ni—Co—P electroless plating film has been proposed (Non-Patent Document 1). It is known that the Ni—Co—P electroless plating film has a small decrease in hardness up to about 200 ° C. and is excellent in sliding characteristics. However, the hardness at the time of precipitation is as low as about Hv 500 to 650, and in order to obtain Hv 700 or higher, a relatively high temperature heat treatment of 300 ° C. or higher is required. However, in this case, since Ni ₃ P having low toughness is dispersed in the Ni matrix, there is a problem that the toughness of the entire coating is deteriorated. Moreover, in heat-treatable Al alloys and resins, heat treatment at high temperature causes a decrease in hardness, and therefore high-temperature heat treatment cannot be applied. Therefore, it is difficult to use Ni-P and Ni-Co-P coatings themselves for light metals such as Al-based and resin-based sliding parts.

In addition to the above films, Ni-WP, Co-WP, and Co-WB system electroless plating films have also been reported (see Patent Document 1). However, it is necessary to add a large amount of tungsten to these plating films in order to maintain the hardness and sliding characteristics at room temperature and high temperature without performing high temperature heat treatment. However, the addition of a large amount of tungsten in the plating film not only leads to a significant decrease in the plating rate, but also increases the film stress, which may lead to deterioration of the film toughness and eventually to the generation of cracks. For this reason, these films are rarely used industrially for sliding members.
Japanese Patent Laid-Open No. 4-119265 Metal Surface Technology Vol.19, No12, p498-503 (1968)

An object of the present invention is to provide a plating film that has high hardness in a wide temperature range from room temperature to high temperature, is excellent in slidability and toughness, and can be formed at high speed.
Furthermore, an object of the present invention is to provide a mechanical component having a high hardness over a wide temperature range and excellent sliding characteristics, in which the sliding portion is coated with the plating film.

The inventors of the present invention have made extensive studies in order to achieve the above object.
As described above, Ni—Co—P plating is known to have excellent sliding characteristics. Therefore, the present inventors predicted that Ni—Co—P is excellent in high temperature hardness, and attempted to improve high temperature hardness by adjusting the amount of cobalt added to Ni—P plating. However, although Ni—Co—P plating has a low rate of decrease in hardness due to temperature, the hardness at room temperature is low in the first place, and sufficient hardness cannot be obtained over a wide temperature range. Therefore, the present inventors have examined an additive element that increases the hardness of Ni—Co—P plating at room temperature and does not significantly affect the high temperature hardness change of Ni—Co—P. At this time, attention was paid to the following. First, in order not to lower the high temperature hardness and toughness during heating, it is difficult to form an intermetallic compound with Ni as the main component, in other words, an element having a high solid solubility from Ni to Ni in the low temperature to high temperature region, In order to improve the hardness, attention was paid to an element having a large atomic number, that is, a large strain. As a result of intensive studies in consideration of these points, it was found that the addition of a predetermined amount of W can improve the hardness at room temperature without adversely affecting the hardness change at high temperatures. The present invention has been completed based on the above findings.
That is, the means for achieving the above object is as follows.
[1] Electroless nickel plating characterized by containing 1 to 50% by weight of Co, 1 to 20% by weight of W and 1 to 4% by weight of P , and the balance of Co, W and P being Ni Film.
[2] The electroless nickel plating film according to [1], wherein the micro Vickers hardness at 25 ° C. is in the range of 700 to 900 and the micro Vickers hardness at 400 ° C. is in the range of 300 to 400.
[3] The electroless nickel plating film according to [2], wherein the micro Vickers hardness at 200 ° C. is in the range of 650 to 750.
[4] A machine part having a sliding part, wherein at least the sliding part is coated with the film according to any one of [1] to [3].

  According to the present invention, it is possible to provide an electroless nickel plating film having both high room temperature hardness and high temperature hardness, and excellent in slidability and toughness.

Hereinafter, the present invention will be described in more detail.
The electroless nickel plating film of the present invention contains 1 to 50% by mass of Co, 1 to 20% by mass of W, and 1 to 4 % by mass of P. The balance of Co, W, and P in the electroless nickel plating film of the present invention is Ni.
In the electroless nickel plating film of the present invention, the W content is 1 to 20% by mass. In the electroless nickel plating film, W is thought to contribute to room temperature hardness improvement, but if the W content is less than 1% by mass, the desired room temperature hardness improvement effect cannot be obtained. On the other hand, if the W content exceeds 20% by mass, the plating rate is remarkably reduced, and W is a rare metal, leading to an increase in cost. W content becomes like this. Preferably it is 2-10 mass%, More preferably, it is 3-5 mass%.

  When the Co content in the electroless nickel plating film of the present invention is less than 1% by mass, the high temperature hardness is degraded, and when it exceeds 50% by mass, the room temperature hardness is degraded. The Co content in the electroless nickel plating film is preferably 10 to 50% by mass, more preferably 20 to 40% by mass.

In the electroless nickel plating film of the present invention, the P content is 1 to 4 % by mass. When the P content is less than 1% by mass, the plating rate and the room temperature hardness are reduced. On the other hand, when the P content exceeds 5% by mass, the number of amorphous regions increases, resulting in a decrease in hardness during precipitation. P content is 1-4 wt%, more preferably from 2 to 3 wt%.

The electroless nickel plating film of the present invention can be obtained by adding a phosphorus compound as a reducing agent and a cobalt compound and a tungsten compound as additives to a nickel salt to precipitate an alloy. As the cobalt salt and nickel salt, for example, sulfate, chloride, acetate, carbonate and the like can be used. As the phosphorus compound of the reducing agent, for example, sodium hypophosphite, potassium hypophosphite, nickel hypophosphite and the like can be used. As the tungsten compound, sodium tungstate, potassium tungstate, or the like can be used. The ratio of nickel salt / phosphorus compound / tungstate / cobalt salt in the plating bath can be appropriately adjusted according to the composition of the plating film. The concentration of each component can be determined in consideration of bath stability and deposition rate. For example, the Ni ion concentration is 0.03 to 0.1 mol / L, the Co ion concentration is 0.01 to 0.05 mol / L, the WO ₄ ion concentration is 0.01 to 0.05 mol / L, and the phosphorus compound of the reducing agent The concentration of can be 0.15 to 0.30 mol / L.

  In consideration of stability and pH buffering action, an organic acid such as acetic acid, malic acid, and citric acid, and a chelating agent such as ethylenediaminetetraacetic acid can be added to the plating bath. Moreover, a trace amount lead compound, a bismuth compound, an indium compound, an antimony compound, a sulfur compound, etc. can be added as a bath stabilizer. Further, the plating bath is preferably adjusted to a pH range of 7 to 8 in consideration of the stability of the bath and the deposition rate.

  The plating film of this invention can be formed by immersing the to-be-plated surface of a base material in the said plating bath for a fixed period. The temperature of the plating bath can be determined in consideration of the stability of the bath and the deposition rate, and can be, for example, in the range of 70 to 95 ° C, preferably 85 to 92 ° C. The surface to be plated of the base material is preferably subjected to a pretreatment performed in a normal plating step before being immersed in the plating bath. Examples of such pretreatment include degreasing using a solvent or an alkaline solution, zinc substitution treatment, and acid dipping treatment.

  A plating film containing a predetermined amount of phosphorus, cobalt and tungsten can be formed by the above electroless plating. Furthermore, the nickel plating film obtained above can improve adhesion and film hardness by heat treatment. The heat treatment conditions can be determined in consideration of the hardness required for the coating and the heat resistance of the base material. The heat treatment range can be set to a range of 150 to 450 ° C., for example. If it is 150 degreeC or more, the improvement effect of film hardness or adhesiveness can fully be acquired. However, if it exceeds 450 ° C., the film hardness may decrease. The heat treatment temperature is preferably in the range of 200 to 400 ° C. The heat treatment time can be determined in consideration of the treatment temperature, the hardness required for the coating, the heat resistance of the base material, the productivity, and the like, and can usually be 30 to 120 minutes. The atmosphere for the heat treatment can be air, an inert gas, a reducing gas, or the like, and can be appropriately selected in consideration of workability and cost.

  The electroless nickel plating film of the present invention can exhibit high hardness at both room temperature and high temperature. In addition, although the heat processing was performed in the conventional plating film for the hardness improvement, the electroless nickel plating film of this invention can show high hardness in both room temperature and high temperature, without heat processing. Regardless of the presence or absence of heat treatment, the micro Vickers hardness of the electroless nickel plating film of the present invention at 25 ° C. is, for example, 700 to 900, preferably 750 to 850. Moreover, the electroless nickel plating film of this invention can show the micro Vickers hardness of 300-400, for example in 400 degreeC irrespective of the presence or absence of heat processing. Furthermore, the electroless nickel plating film of this invention can also show the micro Vickers hardness of 650-750, for example in 200 degreeC irrespective of the presence or absence of heat processing. Thus, the plating film excellent in high temperature hardness is suitable for the surface treatment of the sliding component which becomes high temperature at the time of sliding. In addition, it is also possible to heat-process the electroless nickel plating film of this invention, and, thereby, room temperature hardness and high temperature hardness can be improved.

  Furthermore, the plating film of the present invention has high room temperature hardness and high temperature hardness, and can also exhibit excellent toughness. The conventional plating film has a problem that the toughness is lowered by the heat treatment to improve the hardness, and it has been difficult to achieve both toughness and hardness. On the other hand, the electroless nickel plating film of the present invention can exhibit high toughness with a crack generation load of 20 to 100 N, for example. In particular, the electroless nickel plating film of the present invention can exhibit high hardness at both room temperature and high temperature without heat treatment. In this case, since there is no toughness reduction due to heat treatment, for example, a crack generation load of 50 N or more. Excellent toughness. In addition, since the electroless nickel plating film of the present invention has a small decrease in toughness due to heat treatment, the plated film after heat treatment exhibits high hardness at both room temperature and high temperature, and has good toughness such as a crack generation load of 20 N or more. Can show.

  Examples of the base material on which the plating film of the present invention is applied include iron alloy and aluminum alloy machine parts. However, the present invention is not limited to these, and any article that can utilize the characteristics of the plating film of the present invention can be used as a base material. In particular, since the plating film of the present invention can form a film with high hardness by heat treatment at a relatively low temperature, it can be applied to heat-treatable aluminum alloys or parts based on resin. Is suitable. In particular, as described above, high hardness at 200 ° C. means that the base material hardness is lowered by heat treatment at or near the tempering temperature (about 200 ° C.) after the solution heat treatment of the heat treatment hardening type aluminum alloy. This is a great advantage in that it can exhibit high hardness.

  Furthermore, according to the present invention, it is possible to provide a mechanical component having a sliding portion, in which at least the sliding portion is coated with the plating film. As described above, since the plating film of the present invention is excellent in high temperature hardness, it is suitable for application to a sliding portion exposed to high temperature.

Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the embodiments shown in the following examples.

[Example 1]
As an electroless plating bath, an appropriate amount of a stabilizer added to the following plating solution was used.

Nickel sulfate 18.4g / L
Cobalt sulfate 8.4g / L
Sodium tungstate 12.55g / L
Citric acid 21.0g / L
Propionic acid 22.8g / L
β-alanine 1.78 g / L
Boric acid 30.9g / L
Sodium hypophosphite 23g / L
Thiodiglycolic acid 10ppm

The electroless plating bath was adjusted to pH 7.5 with caustic soda and then heated to 90 to 92 ° C. A test piece (24 × 50 × 3 mm) made of A6061 was put into this bath. The test piece was subjected to the following pretreatment before being put in.

(1) Weak alkaline degreasing 40 ° C., 1 minute (sodium carbonate 20 g / L, sodium tripolyphosphate 20 g / L, residual water)
(2) Washing with water (3) Etching 20-25 ° C, 30 seconds (nitric acid 67.5%) 90%, hydrofluoric acid (50%) 20%, water 10% (4) water washing (5) Zinc replacement treatment 20-25 ℃, 30 seconds (caustic soda 120g / L), zinc oxide 20g / L, ferric chloride 2g / L, Rochelle salt 50g / L, ammonium nitrate 1g / L
(6) Acid immersion (nitric acid 10%) 20-25 ° C., 1 minute (7) Washing with water (8) Zinc replacement treatment (same as (5) above)
(9) Washing with water (10) Plating solution SC-93 (trademark: manufactured by Nihon Kanisen Co., Ltd.) for 30 minutes

  After being immersed in the electroless plating bath for about 2 hours and 20 minutes, the resulting plating film thickness was about 40 μm and the plating rate was about 17 μm / h. Further, the obtained plating film was subjected to component analysis using an energy dispersive X-ray analyzer. As a result, Ni was 66.1% by mass, Co was 28.0% by mass, P was 2.2% by mass, and W was 3.7% by mass.

[Example 2]
A test piece plated under the same conditions as in Example 1 was prepared and heat-treated at 200 ° C. for 1 hour in an electric furnace (in the atmosphere).

[Comparative Example 1]
As an electroless nickel plating bath, SK-100 solution (trademark: manufactured by Nippon Kanisen Co., Ltd.) diluted 5-fold with pure water was used. After adjusting the pH to 4.5, the plating bath was heated to 90 ° C. A test piece (24 × 50 × 3 mm) made of the same A6061 material as used in Example 1 was put into this bath after the same pretreatment as in Example. Thereafter, in order to adjust the film thickness to about 40 μm, it was immersed for about 2 hours and 20 minutes as in the example. The test piece thus prepared was heat treated at 320 ° C. for 2 hours in an electric furnace (in the air) as Comparative Example 1. It was P: 8 mass% (remainder: Ni) when the composition of the obtained plating film was analyzed using the energy dispersive X-ray analyzer.

[Comparative Example 2]
As an electroless nickel plating bath, S-795 solution (trademark: manufactured by Nippon Kanisen Co., Ltd.) was used. After adjusting to pH 6.0, the bath temperature was warmed to 90 ° C. A test piece (24 × 50 × 3 mm) made of the same A6061 material as used in Example 1 was added to this bath after the same pretreatment as in Example 1. Thereafter, in order to adjust the film thickness to 40 μm as in the example, it was immersed for about 2 hours and 20 minutes. When the composition of the obtained plating film was analyzed using an energy dispersive X-ray analyzer, it was P: 2 mass% (remainder: Ni).

[Comparative Example 3]
As an electroless nickel plating bath, SKB-200-1, SKB-200-2, SKB-200-4, and SKB-200-5 (trademark: manufactured by Nippon Kanisen Co., Ltd.) were used. These liquids were mixed at a predetermined composition and adjusted to pH 6.2, and then the bath temperature was heated to 82 ° C. A test piece (size) made of the same A6061 material as used in Example 1 was put into this bath after the same pretreatment as in Example. Thereafter, as in Examples 1 and 2, the film was immersed for about 2 hours and 10 minutes in order to adjust the film thickness to 40 μm. When the composition of the obtained plating film was analyzed using an energy dispersive X-ray analyzer, it was P: 2 mass%, B: 0.2 mass% (remainder: Ni).

[Comparative Example 4]
As an electroless plating bath, an appropriate amount of a stabilizer added to the following plating solution was used.
Table 2 Nickel sulfate 18.4g / L
Citric acid 21.0g / L
Propionic acid 22.8g / L
β-alanine 3.56 g / L
Boric acid 30.9g / L
Sodium hypophosphite 25g / L
Thiodiglycolic acid 100ppm
Cobalt sulfate 8.43 g / L

  The plating bath was adjusted to pH 7.15 with caustic soda and then heated to 85 to 87 ° C. A test piece (size) made of the same A6061 material as used in Example 1 was put into this bath after the same pretreatment as in Example. Thereafter, as in the example, the film was immersed for about 3 hours and 20 minutes in order to adjust the film thickness to 40 μm. When the composition of the obtained plating film was analyzed using an energy dispersive X-ray analyzer, Co was 35% by mass and P was 2% by mass (remainder: Ni).

Test Example 1: Film Hardness / High Temperature Hardness The hardness at each temperature shown in Table 1 of the films obtained in Examples 1 and 2 and Comparative Examples 1 to 4 was determined using a micro Vickers hardness tester (test load 50 g). The results are shown in Table 1.

Test Example 2: Toughness For each of the samples of Examples 1 and 2 and Comparative Examples 1 to 4, the diamond cone was pressed against the surface of the film and swept while increasing the load continuously. More crack generation load was detected. A film having a high crack generation load is a film having excellent toughness. The results are shown in Table 2.

Test Example 3: Sliding property (25 ° C.)
The friction coefficient was measured by placing each sample of Examples 1 and 2 and Comparative Examples 1 to 4 on a heatable operation table and pressing and sweeping the SUJ sphere against the surface of the coating. The diameter of SUJ was 3/16 inch and the applied load was 200 g. Furthermore, it slid several times and the friction coefficient after 50 times of sliding was also measured. The measurement was terminated when the friction coefficient exceeded 0.3, and the number of slidings at that time was defined as the number of seizures. It can be said that a film having a low coefficient of friction and a large number of baking slides has a higher slidability. The results are shown in Table 3.

Test Example 4: Sliding property (200 ° C)
For each sample of Examples 1 and 2 and Comparative Examples 1 to 4, the friction coefficient and the number of seizure slides were measured in the same manner as in Test Example 3 except that the measurement was performed while heating the sample to 200 ° C. The results are shown in Table 4.

  The electroless nickel plating film of the present invention is suitable as a surface treatment for sliding parts.

Claims (4)

An electroless nickel plating film comprising 1 to 50% by mass of Co, 1 to 20% by mass of W, 1 to 4% by mass of P , and the balance of Co, W and P being Ni . The electroless nickel plating film according to claim 1, wherein the micro Vickers hardness at 25 ° C is in the range of 700 to 900, and the micro Vickers hardness at 400 ° C is in the range of 300 to 400. The electroless nickel plating film according to claim 2, wherein the micro Vickers hardness at 200 ° C is in the range of 650 to 750. It is a machine part which has a sliding part, Comprising: The machine part which coat | covered at least the said sliding part with the membrane | film | coat of any one of Claims 1-3.